Method of extracting lead from its sulfides



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Patented Nov. Z4, 1953 METHOD oF EXTRACTNG LEAD Faoin Irs sULrmEslCharles B. Foster, Mankayan, Mountain, Republic of the PhilippinesApplication January 22, 1952, Serial No. 267,557 y12 claims. (ol. `75 77This invention relates to an improved method of reducing lead from itssulfide, and is a continuation in part of my copending application,Serial No. 787,286, filed November 21, 1947, now abandoned.

Lead ore most frequently appears in nature in the form of a sulfide(PbS) termed Galena. At present the mined ore usually undergoes certainconcentrating processes whereby a good proportion of the impurities inthe ore are re moved and the ultimate product is a high-grade, iinelydivided concentrate having a lead sulfide content of between 63% tonearly 100%.

Metallurgists have long known that introducing air or oxygen into moltenlead causes a chemical reaction with considerable evolution of heat:

2Pb-l-O2=2Pb0 (exothermic) resulting in a hot molten mixture of lead andlead oxide. If Galena is introduced into this bath, the lead oxidereacts with the lead suliide, producing sulphur dioxide gas and moltenlead,

The heat which is evolved by the partial oxidation or combustion of thelead is of such intensity that no outside fuel or other heating agentneed be added or employed to complete the double decomposition process.The socalled yScotch hearth, Newman hearth, and ore hearth processes,for example, utilize to a slight extent the reaction to furnish heat forthe double decomposition reactions. Heat is also evolved by the primaryreactionsof ore oxidation as follows:

mass is rabbled (agitated) to break up fused p pieces and crusts. Freshlead sulde ore is then introduced on top of the burning mass. This freshore and, to some extent, the hot carbon particles and evolving carbonmonoxidegas, re-

actv with vthe partially oxidizedore .to produce v The metallic lead soformed trickles down through the mass to form a pool on which the chargefloats andthe sulfur dioxide 'and carbon dioxide rise as gases out ofthe charge. Molten metallic lead is periodically tapped, slag particlesare periodically removed from the surface of the molten lead and freshcharge is added as required.

The Scotch hearth process, although taking some advantage of the naturalreducing and c-aloriilc powers of the sulfide ore, has been provenunsatisfactory in several respects, among which are namely:

The process generally involves use of an open hearth, 'and even thoughmechanical instead of human operating means are employed to skim the'floating slag from the top of the bath, and even though the iiues areso arranged as to carry olf most of the gases and dust, a considerableamount of such volatile material escapes into the surrounding air,making it an extremely unpleasant neighborhood in which to work and alsoan extremely dangerous one because of the likelihood of lead poisoningto human beings who may inhale the escaped fumes.

No completely satisfactory means of accurately regulating the properamount of air and therefore the subsequent amount of oxidation takingplace within the bath has been devised.

The high-grade, finely divided lead concentrates which are available`commercially today are not entirely suited to be employed in the Scotchhearth process because the blast of air through the ore causes thefinely-divided partioles' of ore to be lost up the flue or in thesurrounding air as a dust loss.

lThe necessity of forcing air under pressure through the hot ore chargealso causes an important proportion of the lead and a large proportionof the silver usually associated with lead ores to volatilize and becarried away as fumesv in the evolved gases. This results, unlesselaborate precipitation equipment is installed, in a serious loss oflead and such a low recovery of silver that the process is notapplicable to ores having an important content of this metal.

. A great' deal of hand labor is generally neoessary to operateaconventional Scotch hearth.

and because of inaccurate mechanical means so far developed to controlthe chemical reaction, successful operation, of the plant isconsiderablyy dependent upon the personal skill and judgment of itsoperators.

In the instant invention I have provided amethod wherein the chemicalreaction as above set forth. takes place entirely within a closedcircuit, wherein all dust, fumes, and gases are captured without thepossibility of any of them escaping from without the enclosure into theopen air. Thusy not only have yI greatly minimized the risk and dangerof lead poisoning for personnel working within the neighborhood o1 theplant, but I have also provided a means whereby the costly dust andsilver loss is reduced to a minimum. Furthermore, because 'I am able tomechanically control with great accuracy the chemical reactions takingplace in the process, I am not so dependent upon the personal slzill andjudgment of the plant operator as is the case in operating a Scotchhearth.

Although recovery in a blast furnace is the most commonly employed meansof extracting lead from its ores, there vare inherently multipledisadvantages attendant in employing this system, which my invention aspresently described will entirely abrogate or greatly minimize.

In conventional and current lead-blast furnace practice, a Quantity ofthe ore, Galena, is roasted at a reduced heat in the sintering plant.This process. is not only costly, but results in a considerable dustloss. Furthermore, the actual sulfide of the ore combines with theoxygen in the air to form primarily lead oxide (PbO) and sulphur dioxide(SO2) along with smaller amounts of lead sulphate (PbSOi). Thus, theelimination of the sulphur existing `inthe form of a suliide duringsintering Wastes the natural reducing power and caloric 'power of theGalena, thus making necessary the later use of carbon in some form toserve as a reducing agent and also as a `fuel during the actualsmeltering of the ere in the blast furnace at a high temperature.

The extreme neness of present day high-grade ore concentrate is notsuited for use in a blast furnace because of increased dust loss aswellas clogging of the blast furnace when such finelydivided concentrate issubjected to the air blast in the furnace. One of the objects insintering the ore is to provide a coarse, porous product suitable foruse within the blast furnace.

Although currently available lead ore concentrates are very high-grade,it has been found economically and practically expedient to ex cessivelydilute this concentrate before considering it suitable for introductioninto a blast fur nace.

Furthermore, the sulphur dioxide gas which is evolved at the sinteringplant is so highly diluted with surplus air that even after removal ofdust and volatile impurities it is not generally considered commerciallyfeasible to utilize this gas in acid manufacture.

Further disadvantages attendant with blast furnace operations are thatthe initial installation involves. a large capital investment generallycontemplating additional detached plants for the manufacture ofintermediate and by-products, and also the fact that the starting andshutting down of blast furnaces is costly and results in a considerabletime loss.

The instant invention is designed speciilcally to overcome theseobjections applicable to bla-st furnace operation. For example,sintering Vthe ore is both unnecessary and undesirable in practicing mymethod. Therefore, the natural reducing and caloric power of the suldeore is not lost by sintering, but is fully preserved and utilized to theutmost extent as hereinabove pointed. out. Furthermore, the fineness ofpresent day ore concentrate is especially suited for use in my processas the more nely divided the particles of ore, the more readily andcompletely will they react with the molten lead oxide. Again. thecurrent high-grade ore concentrate may be employed without .dilution inpracticing my process, and furthermore the relatively undiluted Sulphurdioxide gas which is given off during the reaction may "be 'subsequentlyrecovered for suitable acid manufacture. It should also be pointed `outthat both the initial installation cost and the cost of starting andstopping my apparatus is much less than the installation and/oroperating cost for a conventional type blast furnace.

A principal object of this invention is to provide a new and practicalmethod of lead reduction which utilizes to great advantage currentlyavailable, relatively high-grade quality, lead ore concentrates in thereduction process without the necessity of excessively diluting the saidcon centrates.

Another object of this invention is to provide a-continuous, thermallyself-sustaining method of metal reduction which requires no application'of external heat to `accomplish the reduction of metal from itsconcentrate after operations have been commenced, as will more fullyappear hereinafter.

Another object of my invention is to provide a method which utilizes thenatural self-contained calorific properties and the natural reducingpower of simple sulfide ore concentrates to accomplish the reduction ofmetal therefrom.

Another object of this invention is to provide a method which takes fulladvantage of currently1 available, high-grade sulde ore concentrates byintroducing them into a reaction chamber without expensive dust lossand/or without the necessity of providing for large and expensiveinstallations for dust recovery.

Another object of the invention is to provide a method vwhich may bepracticed in an apparatus which is relatively inexpensive to install andto operate as compared to cost of installation and operation of knowntypes of apparatus in more or less common usage today, as above mentioned.

Another object of my invention is to produce as a by-product a highlyconcentrated sulphur dioxide gas suitable for acid manufacture.

Further objects of my invention will become apparent upon the reading ofthe specification and referring to the accompanying drawings in whichsimilar characters of reference represent corresponding parts in each ofthe several views.

In the drawings:

Fig. 1 is a schematic view of a suitable ap paratus in which the processmay be practiced.

Fig. 2 is a sectional View taken on line 2 2 of Fig. l.

Fig. 3 is an enlarged perspective view of the impellor incorporated inthe apparatus.

Fig. 4 is a top plan View of a preferred em bodiment of the apparatus.

Fig. 5 is a sectional View taken on line 5--5 of Fig. 4.

Fig. 6 is a sectional view taken on line i5 of Fig. 4.

In accordance 'with the present invention I Standards, part il,Non-Ferrous Metals, page .1.016, published in 195o. The iinely-dividedore or concentrate, red into reaction chamber I3 by screw feeder l5,mixes with and chemically unites with the lead oxide carried along as apart of the molten mixture, as hereinabove clescribed. Baines is,similar to baiiies Il, are provided to insure a thorough mixing of themolten mass and lead sulfide together and thereby insure a more completechemical reaction between the lead sulde and the lead oxide. This latterchemical reaction is violent and produces metallic lead and sulfurdioxide gas as illustrated in the following chemical equation:

PbS+2PbG=2Pb+SOz [is above ind ated, the screw feeder permits thefinely-divided PbS to be fed into the reaction chamber at apredetermined regulated rate of flow, The amounts PbS continuouslyintroduced into the reaction chamber for reaction with the PbO should,of course, preferably be substantially in proportions for a balancedvequation in a reaction between the lead suliide contained in the ore andthe lead oxide. It will be recalled that the PbO carried along in themolten stream was itself produced through controlled oxidation oi apredetermined fractional part of the original metal bath, and,therefore, the total amount of PbO available for reaction with the PbSis readily ascertainable.

It is also preferable to introduce into the reaction chamber along withthe lead sulde concentrate, relatively small quantities ci a suitableux, such as limestone, lime, or soda ash, for

example, which will react with contained silica impurities in theconcentrate to form relatively fusible slag. Increased fusbility of theslag will, of course, minimize metal loss through its inclusion withinslag ultimately removed from the bath.

Residual diluent gases from the oxidizing chamber and evolved sulphurdioxide, intermixed with hot molten metallic lead and nongaseousimpurities, leave reaction chamber i3 through discharge conduit ll' andare introduced into the vortex of a closed impellor, such as indicatedat la, which is adapted to operate within roof enclosed agitationchamber I9. Violent intermixing created by agitation of the irnpelloi`favors the completion of the reactions in the reaction chamber and theformation of a clean and fluid slag. The agitation also causes theintermixed gases to rise through the molten lead contained in chamberi9. The escape of these gases is prevented by means of a hood whichcovers the agitation chamber.

The impellor, heretofore indicated at it, may be of generallyconventional constructionA and is shown as being of a type commonly usedin ore notation process apparatus. More specifically, this type ofimpellor comprises a pair of oppositely disposed, spaced, circularplates Z and 2l housing a plurality of radial iins 22. An upper tubularcasing 23 dening an enlarged inlet mouth 2o in flow communication withthe interior of the impellor provides an opening through which driveshaft 2.5, which is. anchored at 26 to bottom plate 2l, may project.upwardly. Shaft 25, in turn, may be rotated by means of a motor 2l, orother driving means, located outside of agitation chamber I9.

Rotation of the impellor will continuously centrifugally force outwardlythe molten mass and contained gas introduced into mouth 24. of

the impellor from conduit Il. The impellor functions to continuouslysuck downwardly into agitation chamber i9 the materials from reactionchamber I3 and prevent back-pressure from building up in the system byvirtue of the SO2 gas produced in chamber I3. Moreover, as abovesuggested, the impellor creates a turbulent agitation within chamber I9and thus serves to insure a thorough mixing and reaction between anyunreacted PbO and PbS iiowing from the reaction chamber I3. A suitableflue 30 supported by hood 3| conducts the gases to a point of suitabledisposal. The sulfur dioxide concentration in these gases isexceptionally high, and it may therefore be inexpensively recovered foruse in the manufacture of sulfuric acid, liquid sulfur dioxide, or othercommercial by-products.

The agitation chamber is provided with a port 32 through which solidparticles of slag may be removed from the surface of the bath at suchintervals or under such conditions as this may become necessary. Thisport is provided with a hinged gas-tight door 33 so that under normaloperating conditions no gas can escape through said port.

From the agitation chamber the liquid mixture oi molten lead and moltenslag together with suspended solid particles is conducted through asuitable conduit 34 into storage reservoir 2.

The lead reservoir tank 2 is a quiet zone which permits the separationby gravity of the molten lead from its molten and solid impurities. Atone side of this reservoir is a lead well 35 in communication with thereservoir via opening 35i and from which molten lead may be continuouslyor intermittently withdrawn, as through port 31, at a rate substantiallyequivalent to the rate of entry into the system of the contained lead inthe sulde ore. The reservoir is likewise provided wtih a slag tap hole38 through which accumulated slag may be perodically tapped from thesurface of the lead. Within this reservoir and taking its feedtherefrom, is variable-speed, centrifugal pump 4, heretofore designated.This pump continuously pumps molten lead to the oxidation chamber, thusclosing the circuit and making this a cotninuous cyclic process.

As heretofore stated, it is a principal object of the present inventionto teach and to provide a continuous and thermally self-sustainingcycle-process of metal reduction. In the cyclic process just described,and as stated heretofore, the exothermic oxidation reaction:

y no extraordinary, elaborate, or unusual precautions need. be taken tomaintain the necessary heat. balance betwen the reactions sufcient tomaintain a caloriiic self-sustaining continuous process.

Although it is not essential to use any particular type of material inconstructing the instant apparatus, other than a material which cansuitably withstand the various temperatures and chemical reactionstaking place during the process as above enumerated, I prefer to use asmy construction materials. ceramic rerractories for reaction chamberlinings and heavy cast iron, similar to that used in common leadrefining kettles, for the reservoirs and pump parts. Not only can castiron ci this type endure the temperatures, pressures and chemicalreactions pron duced during the process, but such material upon oncebeing brought up to proper temperature has a marked tendency to hold andretain the heat imparted to it. ribis tendency is especially valuable inmy process for the reason that the apparatus may be stopped or shut downfor a period of several hours while retaining sufficient heat to preventthe molten lead from cooling and solidiiying. Shouldthe lead solidify inthe tanks or conduits during a shut-down, it is only necesary to heatthe equipment by oil burners and blow-torches as earlier described,until the meta-l assumes a molten forni. The pump and inipellor may thenbe started and when the lead is freely circulating within the system,the procinay be cotninued oeiore and as above described.

Although l have described the present invention in come detail forpurposes of illustration and example, it is understood that variouschanges modifications may be practiced within the spirit or' theinvention scope of the appended claims.

l claim:

l. in method of reducing lead from relatively h" .li-grade undilutedlead sulfide ore, the successive steps comprising, forming a molten ofrelatively pure lead, continuously cir- 'ng said molten bath of leadfrom a startet oxygen in an amount substantially will oxidize the entirequantity or said molten bath, whereby a molten lnixture c iprisingpredetermined amounts of molten lead and lead oxide formed, duringcontinuous circulation through a second chamber introducing into saidmolten mixture for reaction w i said lead oxide amounts of ne irelatively high-grade, undiluted lead Cdilation in reaction between saidpredeter-mined amount of lead oxide and the lead sulcontained in saidore, whereby there ene. chemical reaction resulting in the production ofa rcolten mixture of molten lead and sulphur diox le gas, removing saidsulphur di.. o'ficle said rnoltel'l niixture, and then dating part csaidlead back to said first chamber recirculation baci through said ofchambers and removing a part of said metal for recovery.

fl method or reducing lead from relatively undilute1 sulfide oreaccording to claim l and wherein the amount oi oxidizing gas than thearncunt of said gas one-half ci entire quantity circulating through saidiirst 5. Amethod of extracting lead from its sulde which comprises;providing a mass of lead in la molten condition, providing also a massof predominantly lead sulfide, introducing the moltenA lead into anoxidation zone, and also introducing in said oxidation zone an oxidizingagent in quantity suicient to oxidize a substantial proportion of thelead to its oxide according to the exothermic reaction 2Pb+O2=2PbO,introducing the molten mass of lead and oxidized metal to a reductionzone; adding said lead sulde to the molten 'mass in the reduction zonein quantity sufficient to reduce substantially all of the lead oxideaccording to the endothernlic reaction PbS+zPbO=3Pb+Oz; separatingsulphur olioxide from the reduced mass; and returning a surliclentquantity of molten metal from the reduction Zone to the oxidation zoneto maintain a body or" molten, circulating and reaction medium lorcontinued operation of the process; said quantity of oxmlzing agentbeing sufficient to provide the heat absorbed in said endothermicreaction and to also maintain the mass in molten condition Without inputof heat from an external source.

6. lhe method of claim 5 wherein the said oxidizing agent introducedinto said oxidation zone comprises molecular oxygen, and wherein theamount or' lead sulllde introduced into said reduction zone is insubstantially stoichiometric proportion to the quantity of molten leadoxidized in said oxidation zone Jfor the said reaction PoS+2PbO=3Pb+SOa7. The method oi' claim 5 wherein the mass of predominately lead sulliuecontains from about 55 U/U to 85% by weight of lead and which is lineenough to all pass through a standard No. 2O sieve.

8. A continuous method of extracting lead from its suliide whichcomprises: providing a mass or' lead in a molten condition; providingalso a mass of predominantly lead sulfide; continuously circulating themolten lead into an oxidation zone, and also continuously introducingmolecular oxygen into said zone in quantity suiicient to oxichze asubstantial proportion or' the lead to its oxide according to theexothermic reaction 2Pb+O2=ZPbO; continuously circulating the fluid massof molten lead and oxidized lead to a reduction Zone; continuouslyadding said lead sulde to the molten mass 1n the reduction zone inquantity sufficient to reduce substantially all of the lead oxideaccording to the endothermic reaction PbS+2PbO=3Pb+SO2g continuouslyseparating sulphur dioxide from the reduced mass and withdrawing aportion of the lead for recovery and continuously recirculating a sufucient quantity of said lead from the reduction Zone to the oxidationzone to maintain a body of molten circulating and reaction medium forcontinued operation of the process; said quantity of oxygen beingsucient to provide the heat absorbed in said endothermic reaction and toalso maintain the mass in molten condition Without input of heat from anexternal source.

9. The method of claim 8 wherein the amount of lead sulfide introducedinto said reduction zone is in substantially stoichiometric proportionto the quantity of molten lead oxidized by said molecular oxygen in saidoxidation zone for the said reaction PbS+2PbO=3Pb|SOa lo. The method ofclaim 8 wherein the mass of predominately lead sulfide contains fromabout 55% to 85% by Weight of lead and Which is ne 11 enough to all passthrough a 'standard No. 20 sleve.

11. The method of extracting lead from its sulfide which comprises:providing a mass of predominantly lead sulfide containing not more thanabout 37% of impurities; providing a mass of molten lead; continuouslyintroducing said molten lead into an oxidation zone; continuouslyintroducng molecular oxygen into said oxidation zone in quantitysufcient to react With not more than 50% of molten lead to form a moltenmass of lead and oxidized lead, continuously circulating said moltenmass into a reduction zone and continuously introducing into said zonesaid lead sulfide in a proportion approximately stoichiometrioallyrelated to the oxygen introduced into the oxidation zone so 'as toapproximately bal'- ance the reactions: 12 @mthferr-F1142)..21Ebir02ll0y continuously removing sulfur dioxide resultingfrom Reaction 2; and continuously recirculating a suiiicient quantity ofmolten lead from the reduction zone to the oxidation zone to maintain acontinuous, cyclic ilow of molten metal; out under conditions to utilizetll'ehe'at evolved ln action 1 the quantity of oxygen introduced intosaid oxidation Yzone being 'such that the heat -generated in Reaction 1Ais sufficient t'o supply the heat absorbed by Reaction 2 and also tomaintain the mass in molten condition Without input of heat from anexternal source. v

12. The method of `claim 11 wherein the mass of predominately leadsulfide contains from about 55% to 85% by Weight of lead and which isfine enough to all pass through a standard No. 20 sieve.

c'HARLEs B. FOSTER.

Referenes cited in the file of this parent UNITED 'STATES PATENTS

1. IN A METHOD OF REDUCING LEAD FROM RELATIVELY HIGH-GRADE UNDILUTED LEAD SULFIDE ORE, THE SUCCESSIVE STEPS COMPRISING, FORMING A MOLTEN BATH OF RELATIVELY PURE LEAD, CONTINUOUSLY CIRCULATING SAID MOLTEN BATH OF LEAD FROM A STARTING POINT THROUGHOUT A SERIES OF CHAMBERS BACK TO SAID STARTING POINT, DURING SAID CIRCULATION THROUGH A FIRST CHAMBER INTRODUCING INTO SAID MOLTEN BATH AN OXIDIZING GAS CONTAINING A KNOWN QUANTITY OF OXYGEN IN AN AMOUNT SUBSTANTIALLY LESS THAN WILL OXIDIZE THE ENTIRE QUANITITY OF SAID LEAD IN SAID MILTEN BATH, WHEREBY A MOLTEN MIXTURE COMPRISING PREDETERMINED AMOUNTS OF MOLTEN LEAD AND LEAD OXIDE IS FORMED, DURING SAID CONTINUOUS CIRCULATION THROUGH A SECOND CHAMBER INTRODUCING INTO SAID MOLTEN MIXTURE FOR REACTION WITH SAID LEAD OXIDE AMOUNTS OF FINELY-DIVIDED, RELATIVELY HIGH-GRADE, UNDILUTED LEAD SULFIDE ORE SUBSTANTIALLY IN PROPORTIONS FOR A BALANCED EQUATION IN A REACTION BETWEEN SAID PREDETERMINED AMOUNT OF LEAD OXIDE AND THE LEAD SULFIDE CONTAINED IN SAID ORE, WHEREBY THERE ENSUES A CHEMICAL REACTION RESULTING IN THE PRODUCTION OF A MOLTEN MIXTURE OF MOLTEN LEAD AND SULPHUR DIOXIDE GAS, REMOVING SAID SULPHUR DIOXIDUE GAS FROM SAID MOLTEN MIXTURE, AND THEN CIRCULATING A PART OF SAID LEAD BACK TO SAID FIRST CHAMBER FOR RECIRCULATION BACK THROUGH SAID SERIES OF CHAMBERS AND REMOVING A PART OF SAID METAL FOR RECOVERY. 